The present invention relates to an image forming device for processing photosensitive media, wherein the photosensitive media includes a plurality of microcapsules that encapsulate imaging material such as coloring material. More specifically, the present invention relates to an image-forming device that includes a photobleach system that is adapted to eliminate or minimize undesired coloration in a final print.
Image forming devices are known in which media having a layer of microcapsules containing a chromogenic material and a photohardenable or photosoftenable composition, and a developer, which may be in the same or a separate layer from the microcapsules, is image-wise exposed. In these devices, the microcapsules are ruptured, and an image is produced by the differential reaction of the chromogenic material and the developer. More specifically, in these image-forming devices, after exposure and rupture of the microcapsules, the ruptured microcapsules release a color-forming agent, whereupon the developer material reacts with the color-forming agent to form an image. The image formed can be viewed through a transparent support or a protective overcoat against a reflective white support as is taught in, for example, U.S. Pat. No. 5,783,353 and U.S. Publication No. 2002/0045121 A1. Typically, the microcapsules will include three sets of microcapsules sensitive respectively to red, green and blue light and containing cyan, magenta and yellow color formers, respectively, as taught in U.S. Pat. No. 4,772,541. Preferably a direct digital transmission imaging technique is employed using a modulated LED print head to expose the microcapsules.
Conventional arrangements for developing the image formed by exposure in these image-forming devices include using spring-loaded balls, micro wheels, micro rollers or rolling pins, and heat from a heat source is applied after processing to accelerate development.
The photohardenable composition in at least one and possibly all three sets of microcapsules can be sensitized by a photo-initiator such as a cationic dye-borate complex as described in, for example, U.S. Pat. Nos. 4,772,541; 4,772,530; 4,800,149; 4,842,980; 4,865,942; 5,057,393; 5,100,755 and 5,783,353. Because the cationic dye-borate anion complexes absorb at wavelengths greater than 400 nm, they are colored and the unexposed dye complex present in the microcapsules in the non-image areas can cause undesired coloration in the background area of the final print or picture. That is, the print typically exhibits an obvious overall coloration caused by the residual photo-initiator. Typically, the mixture of microcapsules is greenish and can give the background areas a greenish tint. Although exposure to room light will serve to bleach out the photo-initiator over time, the print quality immediately after processing could appear to be of poor quality.
A conventional approach to prevent or reduce this undesired coloration in the background as well as the developed image include reducing the amount of photoinitiator used and adjusting the relative amounts of cyan, magenta and yellow microcapsules. The problem with this approach is that while this can mitigate the unwanted coloration, photobleaching of the photoinitiator must necessarily be much slower than the photobleaching or photo-softening reaction.
Another issue with respect to providing photobleaching relates to robustness and cost. Typically, a conventional compact portable printer for photosensitive microcapsule type print media does not contain user serviceable components and conventional white light sources such as incandescent lamps or florescent tubes may fail and need replacement over the useful life of the printer. Further, the electroluminescent panel in these devices may not provide enough energy to provide a photo-bleaching action, or may be too costly for the printer.
The present invention addresses the above-mentioned drawbacks by providing for an image forming device for processing photosensitive media that includes a plurality of microcapsules, wherein the image forming device comprises a photo-bleach system, mechanism or assembly that is adapted to eliminate or minimize undesired coloration in a final print caused by residual photo-initiators. The present invention further provides for a method of reducing or eliminating undesired overall coloration in a print caused by residual photo-initiators.
The device and method of the present invention involves the construction of a non-image forming second LED print head (a photo-bleaching LED print head) located downstream of an exposure LED print head (with respect to the media conveying direction); and the association of the second LED print head with a processing section and/or the exposure LED print head of the image forming device. The second LED print head comprises at least one R, G, and B LED, wherein each LED is fully on during a photo-bleach step and would not require modulation or specific spot shaping as would be required by an image forming exposure LED print head.
The second LED print head is preferably co-joined to or associated with the processing assembly of the image-forming device to permit a bi-directional scanning of the second LED print head without additional drive components. The second LED print head serves to photo-bleach the print prior to the print exiting the body of the image-forming device to provide for an immediate satisfactory print in which undesired coloration has been bleached out.
The present invention therefore relates to an image forming device which comprises an imaging member adapted to form a latent image on a photosensitive medium, with the photosensitive medium comprising a plurality of microcapsules which encapsulate imaging material; a processing assembly adapted to develop the latent image; and a non-imaging member adapted to apply light onto said developed latent image to apply a photo-bleaching effect to the latent image and reduce overall undesired coloration in the latent image.
The present invention further relates to an image forming method which comprises the steps of exposing a photosensitive medium comprising a plurality of microcapsules which encapsulate imaging material to form a latent image, with the exposing step comprising applying a first light beam onto the photosensitive medium; developing the latent image; and photobleaching the photosensitive medium by applying a second light beam to the exposed and developed photosensitive medium, with said second light beam being adapted to bleach out undesired coloration resulting from the exposing step.
The present invention further relates to an image forming device which comprises an imaging member adapted to form a latent image on a photosensitive medium, with the photosensitive medium comprising a plurality of microcapsules which encapsulate imaging material; a processing assembly adapted to develop the latent image; and a non-imaging member adapted to apply non-visible energy onto the developed latent image to apply a photo-bleaching effect to the latent image and reduce overall undesired coloration in the latent image.
The present invention further relates to an image forming method which comprises the steps of exposing a photosensitive medium comprising a plurality of microcapsules which encapsulate imaging material to form a latent image; developing the latent image; and photobleaching the photosensitive medium by applying non-visible energy to the exposed and developed photosensitive medium to bleach out undesired coloration resulting from the exposing step.